For many years voice telephone service was implemented over a circuit switched network commonly known as the public switched telephone network (PSTN) and controlled by a local telephone service provider. In such systems, the analog electrical signals representing the conversation are transmitted between the two telephone handsets on a dedicated twisted-pair-copper-wire circuit. More specifically, each telephone handset is coupled to a local switching station on a dedicated pair of copper wires known as a subscriber loop. When a telephone call is placed, the circuit is completed by dynamically coupling each subscriber loop to a dedicated pair of copper wires between the two switching stations.
Recently, voice telephone service has been implemented over the Internet. Advances in the speed of Internet data transmissions and Internet bandwidth have made it possible for telephone conversations to be communicated using the Internet's packet switched architecture. In one example, a cable service operator may include a multi-media terminal adapter (MTA) with one or more FXS ports embedded with the DOCSIS cable modem system and use a call management server (CMS) to provide telephone service using IP packets over the operator's hybrid fiber-coaxial (HFC) network.
A problem with use of the Internet's packet switch architecture is that when Internet traffic load is high, packets can be significantly delayed in router buffers or even dropped when router buffers “overflow”. Packet delays and dropped packets significantly degrade audio quality of services (QOS)—well below audio QOS provided by the PSTN.
To improve the quality of service for audio calls with the goal of enabling cable service operators to provide reliable telephone service across their HFC networks, DOCSIS includes a Dynamic Service Flow scheme which dynamically provides dedicated bandwidth at predetermined time intervals to support a media session of a telephone conversation.
In an existing implementation utilizing CableLabs PacketCable 1.0/1.5, DQoS involves the CMS using Common Open Policy Service (COPS) protocol to communicate with the Cable Modem Termination System for resource reservation, and Network Control Signaling (NCS) to instruct the cable modem embedded with the MTA to utilize DOCSIS Dynamic Service Flow messages to request that the Cable Modem Termination System controlling the HFC network allocate and commit sufficient bandwidth, each being referred to as a service flow, for the media session of a telephone conversation.
More specifically, when the MTA detects that a telephone device coupled to one of its FXS ports is taken off hook, NCS signaling is used to notify the CMS of such an event. The CMS, communicates directly with the CMTS to reserve resources for the MTA and uses NCS signaling to instruct the MTA to create the connection and request allocation and commitment of bandwidth for the service flow via the embedded DOCSIS cable modem using DOCSIS Dynamic Service Flow messages.
Utilizing DOCSIS 2.0, up to 14 service flows may be active between an MTA and a CMTS. Utilizing DOCSIS 3.0, up to 24 service flows may be active between and MTA and a CMTS. Further, each of the 24 service flows may support multiple sub flows (also known as multiple grants per interval) with each sub flow supporting a distinct media session—so long as each media session utilizing a sub flow within the same service flow has common service attributes. There exists a maximum number of sub flows supported by DOCSIS 3.0.
In another existing implementation for non-NCS systems, the DQoS resource reservation and commitment are done by network based servers communicating directly with the CMTS under the CableLabs PacketCable Multimedia (PCMM) architecture.
As an advantage, a Cable Modem (CM) without MTA capability may support multiple VoIP devices on a local IP subnet (i.e. a Local Area Network). Each VoIP device may contact the network based server as part of setting up a VoIP session to another VoIP device. The network based server, as part of session set up, instructs the CMTS to establish a service flow (or a sub flow to an existing service flow) to support a media session of a VoIP telephone conversation.
A problem exists in that the DQoS mechanism described above is available only for devices wherein a CMS Server or network based servers in the PCMM architecture are available managing the reservation of bandwidth with the CMTS. DQoS is unavailable for non-NCS VoIP devices which either have an embedded DOCSIS cable modem or may be coupled to a local area network supported by a cable modem.
What is needed is a system and method that enables use of DQoS, including multiple grant per interval technology, by VoIP devices (whether embedded with the cable modem or coupled to the cable modem by a local area network) without requiring NCS messaging with a CMS server or the network infrastructure of PCMM.